1. Field of the Invention
The present invention relates to a plasma display panel apparatus, and more particularly, to a black matrix formed on a front substrate and barrier ribs formed on a rear substrate for improved contrast.
2. Discussion of Related Art
In general, a plasma display panel apparatus includes discharge cells formed between a rear substrate having barrier ribs formed therein and a front substrate opposite to the rear substrate. The plasma display panel apparatus implements images by light-emitting phosphors with vacuum ultraviolet rays generated when an inert gas within each of the discharge cells is discharged by a high frequency voltage.
FIG. 1 is a plan view of electrodes formed in a general plasma display panel. FIG. 2 is a cross-sectional view of a discharge cell of the general plasma display panel.
The discharge cell is formed on a rear substrate 18 opposite to a front substrate 10 by a plurality of barrier ribs 24 partitioning discharge spaces.
An address electrode 12X is formed on the rear substrate 18. Scan electrode 12Y and sustain electrode 12Z are formed in pairs on the front substrate 10. As shown in FIG. 1, the address electrodes 12X cross the scan electrode 12Y and the sustain electrode 12Z. The front substrate 10 shown in FIG. 2 is rotated by 90°.
A dielectric layer 22 for accumulating wall charges is formed on the rear substrate 18 having the address electrodes 12X formed therein.
The barrier ribs 24 are formed on the dielectric layer 22Z, forming the discharge spaces between the barrier ribs. The barrier ribs 24 prevent ultraviolet rays generated by a discharge and a visible ray from leaking to neighboring discharge cells. Phosphors 26 are coated on surfaces of the dielectric layer 22 and the barrier ribs 24.
An inert gas is injected into the discharge space. The phosphors 26 are excited by ultraviolet rays generating during a discharge of the gas, generating one of red, green and blue visible rays.
Each of the scan electrode 12Y and the sustain electrode 12Z formed in the front substrate 10 includes a transparent electrode 12a and a bus electrode 12b. The scan electrode 12Y and the sustain electrode 12Z cross the address electrodes 12X. A dielectric layer 14 and a protection film 16 covering the scan electrode 12Y and the sustain electrode 12Z are also formed on the front substrate 10.
The discharge cell constructed above is selected by a counter discharge between the address electrodes 12× and the scan electrode 12Y, and then has its discharge sustained by a surface discharge between the scan electrode 12Y and the sustain electrode 12Z, thus radiating a visible ray.
Each of the scan electrode 12Y and the sustain electrode 12Z includes a transparent electrode 12a, and a bus electrode 12b, which has a width smaller than that of the transparent electrode and is formed at one side edge of the transparent electrode.
FIG. 3 shows the configuration of a frame that drivers a general plasma display panel.
Referring to FIG. 3, the plasma display panel is driven with one frame being time-divided into several sub-fields having a different number of emissions in order to implement gray levels of images. Each of the sub-fields includes a reset period for initializing wall charges within discharge cells, an address period for selecting a scan line and selecting a discharge cell in the selected scan line, and a sustain period for implementing gray levels depending on a number in which a sustain discharge is generated.
Gray levels that are implemented in the sub-fields including the reset period, the address period and the sustain period are accumulated during one frame. In the case where images are sought to be displayed with 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 seconds is divided into eight sub-fields (SF1 to SF8), as shown in FIG. 3. Gray levels of 2n (n=0, 1, 2, 3, 4, 5, 6, 7) are represented in each sub-field.
The plasma display panel that displays images using the driving method as shown in FIG. 3 improves the contrast ratio through optimization of a waveform applied to each of electrodes or the contrast ratio through the blackening of the front substrate 10. To this end, FIG. 4 shows a cross-sectional view of a discharge cell structure in which a black matrix (BM) is formed.
Referring to FIG. 4, a black matrix 17 is formed between an upper dielectric layer 14 of a front substrate 10 and a protection film 16, and is opposite to barrier ribs 24.
That is, the black matrix 17 is formed in the front substrate 10 so that it is overlapped with the barrier ribs 24 parallel to an address electrode X. Therefore, the black matrix 17 can improve the contrast ratio while not covering the display region through which light is transmitted in each of the discharge cells.
The black matrix 17 in the related art is formed to have substantially the same width as that of the barrier ribs 24 that partition the discharge cells. In the case where alignment is inconsistent when the front substrate 10 is combined with the rear substrate 18, the front substrate 10 or the rear substrate 18 is fluctuated right and left. Therefore, the black matrix 17 is not completely overlapped with the barrier ribs 24 and discharge spaces are covered. As a result, a problem arises because the picture quality is degraded.